1. Field of the Invention
The present invention relates to a mold for fixing a metal block on one of the faces of an ophthalmic lens, the mold including an open mold cavity having a bottom wall and a cylindrical side wall.
2. Discussion of the Background
When manufacturing and preparing ophthalmic lenses, it is known practice to fix a metal block on one of the faces of a lens in order to enable the lens to be mounted on the lens holder of a surfacing machine, an edging machine, or a polishing or clear-polishing machine. This operation is usually performed by means of an apparatus including a mold of the type defined above and by casting a low melting point metal into the cavity of the mold. Such an apparatus is described, for example, in French Pat. No. 2 465 562. As can be seen in FIG. 2 of said French patent, the mold 3 is fitted with a removable ring 7 which includes an annular seat 9 and a cylindrical peripheral rim 11, both of which are coaxial with the axis of the mold cavity. The annular seat 9 is provided to support the face of the lens on which the metal block is to be fixed, whereas the peripheral rim 11 whose inside diameter corresponds to the outside diameter of the lens is provided for centering said lens relative to the mold cavity. It is necessary to provide a plurality of rings for such a prior art mold with the rings having rims of different inside diameters corresponding to the respective existing different diameters of ophthalmic lenses, and the ring needs changing each time the diameter of the lens on which a metal block is to be fixed differs from the diameter of the lens on which a metal block has just been fixed. Such ring changing impedes full automation of this procedure. Further, the above-mentioned rings are relatively expensive items insofar as the inside diameters of their peripheral rims must be machined with relatively high accuracy in order to ensure that the lens is accurately centered relative to the mold cavity.